prefer-spread
Require spread operators instead of .apply()
Before ES2015, one must use Function.prototype.apply() to call variadic functions.
var args = [1, 2, 3, 4];
Math.max.apply(Math, args);
In ES2015, one can use spread syntax to call variadic functions.
/*eslint-env es6*/
var args = [1, 2, 3, 4];
Math.max(...args);
Rule Details
This rule is aimed to flag usage of Function.prototype.apply() in situations where spread syntax could be used instead.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-spread: "error"*/
foo.apply(undefined, args);
foo.apply(null, args);
obj.foo.apply(obj, args);
Examples of correct code for this rule:
/*eslint prefer-spread: "error"*/
// Using spread syntax
foo(...args);
obj.foo(...args);
// The `this` binding is different.
foo.apply(obj, args);
obj.foo.apply(null, args);
obj.foo.apply(otherObj, args);
// The argument list is not variadic.
// Those are warned by the `no-useless-call` rule.
foo.apply(undefined, [1, 2, 3]);
foo.apply(null, [1, 2, 3]);
obj.foo.apply(obj, [1, 2, 3]);
Known limitations:
This rule analyzes code statically to check whether or not the this argument is changed. So, if the this argument is computed in a dynamic expression, this rule cannot detect a violation.
/*eslint prefer-spread: "error"*/
// This warns.
a[i++].foo.apply(a[i++], args);
// This does not warn.
a[++i].foo.apply(a[i], args);
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don’t want to be notified about Function.prototype.apply() callings, you can safely disable this rule.
Related Rules
Version
This rule was introduced in ESLint v1.0.0-rc-1.